High power laser heating of low absorption materials
Abstract
A model is presented and confirmed experimentally that explains the anomalous behavior observed in continuous wave (CW) excitation of thermally isolated optics. Distributed Bragg Reflector (DBR) high reflective optical thin film coatings of HfOâ‚‚ and SiOâ‚‚were prepared with a very low absorption, about 7 ppm, measured by photothermal common-path interferometry. When illuminated with a 17 kW CW laser for 30 s, the coatings survived peak irradiances of 13 MW/cm², on 500 μm diameter spot cross sections. The temperature profile of the optical surfaces was measured using a calibrated thermal imaging camera for illuminated spot sizes ranging from 500 μm to 5 mm; about the same peak temperatures were recorded regardless of spot size. This phenomenon is explained by solving the heat equation for an optic of finite dimensions and taking into account the non-idealities of the experiment. An analytical result is also derived showing the relationship between millisecond pulse to CW laser operation where (1) the heating is proportional to the laser irradiance (W/m²) for millisecond pulses, (2) the heating is proportional to the beam radius (W/m) for CW, and (3) the heating is proportional to W/m∙ tanâ»Â¹(√(t)/m) in the transition region between the two.
Description
The article of record as published may be found at http://dx.doi.org/10.1063/1.4896750
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
Related items
Showing items related by title, author, creator and subject.
-
Numerical simulation of the generation of gravity waves in a frontal zone
Given, Robert Ole (Monterey, California. Naval Postgraduate School, 1972-09);The generation of gravity waves in a frontal zone is investigated with a numerical model. The solutions show that gravity waves can be generated in a frontal zone by the application of a heating function which varies ... -
The effects of sensible heat exchange on the dynamics of baroclinic waves
Haltiner, G.J. (Wiley Online, 1967-05);A diabatic two‐level model with variable static stability is investigated with respect to the dynamic stability and thermal structure of harmonic perturbations. The exchange of sensible heat is assumed to be proportional ... -
Final Technical Report on NSF Grant DES 75-10719, "Tropical Wave Dynamics"
Chang, C.-P (Chih-Pei); Williams, Roger Terry (Monterey, California. Naval Postgraduate School, 1978-03); NPS-63CJ78031This research may be divided into the following three parts: a) waves forced by condensation heating in the troposphere, b) the local barotropic instability produced by a spatially varying basic flow, c) the numerical modeling ...